Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 1989
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989mnras.240..833t&link_type=abstract
Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 240, Oct. 15, 1989, p. 833-880.
Astronomy and Astrophysics
Astronomy
517
Active Galactic Nuclei, Exosat Satellite, Seyfert Galaxies, Sky Surveys (Astronomy), X Ray Spectra, Emission Spectra, Heao 1, Line Spectra, X Ray Sources
Scientific paper
Results are presented from Exosat observations of 48 hard X-ray selected Seyfert-type active galactic nuclei (AGN). These include all 30 of the emission line AGN in the Piccinotti (1981) sample. Combining Exosat LE and ME data has yielded X-ray spectra over the broad energy range 0.1-10 keV. Spectra in the about 2-10 keV range are found to be well described by a simple power law, with a narrow distribution of spectral indices across the sample about a mean energy index alpha = 0.70. Exosat has also revealed a substantial number of sources with complex soft X-ray spectra. Evidence that soft emission components occur in many Seyferts, together with detection of rapid variability in the soft component, provides a quantitative support for an accretion disk model for AGN. Approximately half of the present sample of AGN show low-energy absorption attributable to substantial cold matter within the host galaxy. A few cases show evidence for column variability and reduced low-energy opacity (by photo-ionization). These results and the observed rarity of intrinsic absorption in the higher luminosity sources suggest the absorbing matter lies close to the central continuum source.
Pounds Kenneth A.
Turner Tracey Jane
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